Method and installation for producing an electrode plate, an electrode plate and a rechargeable electrochemical battery

ABSTRACT

The present disclosure relates to a method for producing an electrode plate of a rechargeable electrochemical battery that includes producing a substantially flat lead grid having a plurality of grid bars and a plurality of window-like cutouts formed between the grid bars, introducing an active material into the cutouts and/or onto the grid bars of the lead grid, creating a pattern of slot-shaped depressions in the active material by mechanically impacting the lead grid provided with the active material, where the depressions extend to a depth from the outer surface of the active material. The present disclosure further relates to installation of an electrode plate in a rechargeable electrochemical battery.

The invention relates to a method for producing an electrode plate of arechargeable electrochemical battery in accordance with the preamble ofclaim 1. The invention additionally relates to an installation forproducing such an electrode plate in accordance with claim 9, anelectrode plate in accordance with claim 10 as well as a rechargeableelectrochemical battery in accordance with claim 11.

In general, the invention relates to the field of rechargeableelectrochemical batteries having plate-shaped battery electrodes, alsoknown as electrode plates. Such rechargeable electrochemical batteriesare manufactured in particular as lead-acid batteries. The acid therebyforms a liquid electrolyte. Depending on the embodiment of therechargeable battery, the liquid electrolyte can be unbounded or boundin a fiber-like material. In the latter case, such a rechargeablebattery can be designed as an AGM battery, wherein AGM stands forAbsorbent Glass Mat. In these types of rechargeable batteries, at leastpart of the electrode plates, usually the positive electrode plate, canbe covered by a microglass mat separator, e.g. in the manner of theelectrode plate being wrapped within the microglass mat separator duringits manufacture, similar to gift-wrapping a present.

With these types of rechargeable batteries, it is desirable for theelectrolyte to moisten the electrode plates as quickly and evenly aspossible when the battery is filled with the liquid electrolyte for thefirst time. The capacity of the electrode plates to absorb electrolytecan vary significantly depending on their specific manufacturingtechnology.

The invention is thus based on the task of specifying a method forproducing an electrode plate which exhibits improved electrolyteabsorbency as independently as possible from the manufacturingtechnology used to produce said electrode plate. Further specified is anadvantageous installation for producing an electrode plate as well as anelectrode plate and a rechargeable electrochemical battery having suchan electrode plate.

This task is solved in accordance with claim 1 by a method for producingan electrode plate of a rechargeable electrochemical battery having thefollowing steps performed in the following order:

-   a) producing a substantially flat lead grid having a plurality of    grid bars and a plurality of window-like cutouts formed between the    grid bars,-   b) introducing active material into the cutouts and/or onto the grid    bars of the lead grid,-   c) creating a pattern of slot-shaped depressions in the active    material by mechanically impacting the lead grid provided with the    active material, wherein the depressions extend to a depth from the    outer surface of the active material.

To be noted at this point is that the inventive solution comprises thecreating of depressions in the active material, wherein thesedepressions extend to a depth from the outer surface of the activematerial. Such depressions are for example cracks, particularly pressureor stress cracks in the active material, or however also rift-shapeddepressions created by mechanically impacting the lead grid providedwith the active material. As will be described in greater detail below,the crack structure can be produced in particularly simple and easilyrealized manner when the active material has already at least slightlyhardened. The “outer surface” of the active material, from which thedepressions extend to a depth, thereby substantially corresponds to theouter surface of the active material after the active material has beenintroduced into the cutouts and/or onto the grid bars of the lead grid.

The pattern of slot-shaped depressions created by mechanical impact cansignificantly improve the capacity of the electrode plate to absorbelectrolyte.

Positive electrode plates, in which the lead grid is produced in astamping process, in particular show considerable improvements sincethey otherwise have an active material with relatively smooth surface.Generally speaking, however, the invention can achieve improvedelectrolyte absorbency for any type of electrode plate independent ofmanufacturing technology along with more uniform electrolyte wetting ofthe active material. The invention is therefore also advantageouslyapplicable to electrode plates in which the lead grid is produced forexample by casting. The invention is suited to both positive as well asnegative electrode plates. The invention thus in particular enablesbetter production of rechargeable batteries in which the electrodeplates are pressed together closely within the battery case.

The depressions created by mechanical impact extend to a depth withinthe active material from the outer surface of said active material. Thedepressions thereby form fine cracks as it were in the otherwise ratheruniform surface of the active material. It is advantageous for thedepressions to be at least 0.5 to 1 mm in depth. The depressions canalso completely penetrate the active material; i.e. extend all the waythrough to the lead material of the lead grid, although doing so is notmandatory. The depth of the depressions do not have to be the sameacross the length of the depressions and can also vary among differentdepressions.

The pattern of slot-shaped depressions can be produced in various ways.For instance, a type of press can be used to mechanically impact theactive material. The press can already exhibit the respective raisedstructures which correspond to the depressions to be produced. Whencreating the pattern of slot-shaped depressions on opposite sides of theelectrode plate provided with active material, two presses can also beemployed, between which the electrode plate is arranged. The presses arethen moved toward each other relatively, pressing the electrode platebetween them, whereby a pattern of slot-shaped depressions is producedon both sides of the electrode plate.

The pattern of slot-shaped depressions can also be produced by deformingthe lead grid provided with the active material. This can therebycapitalize on the varying degrees of elasticity to the materials used,namely the lead material and the material of the active material. Inparticular, the pasty active material dries/hardens first such that itbecomes relatively brittle, at least compared to the softer leadmaterial. The lead material can readily follow the deformation movementsduring deformation of the lead grid provided with the active materialwithout being damaged. However, a type of fracturing in the surfacestructure of the active material thereby ensues so that the desiredcrack structure will be formed; i.e. a pattern of slot-shapeddepressions in the active material. Tests have shown that bending thelead grid provided with the active material back and forth once or twicesuffices for the purpose of producing the desired crack structure.

Also a combination of the cited method steps for creating the pattern ofslot-shaped depressions is advantageous. The mechanical impact can beapplied for example by an impacting tool or manually. The pressureexerted in the mechanically impacting of the lead grid provided with theactive material is to be regulated so as to produce just the desireddepressions but not loosen the active material from the lead grid ordamage the lead grid. Since the lead grid itself is relatively soft anddeformable but the active material comparatively brittle, the lead gridwill not suffer damage when the pressure force is correctly set whereascracks will form in the harder active material.

One advantageous further development of the invention provides for thepattern of slot-shaped depressions to only be realized by deformation ofthe lead grid provided with the active material, only by mechanicallyimpacting the active material, or only by a combination of thesealternatives. This enables the pattern of slot-shaped depressions to becreated quickly and efficiently and also keeps the equipment costs incheck. An installation for producing an electrode plate thereby onlyneeds fewer, more economical modifications.

According to one advantageous further development of the invention, thepattern of slot-shaped depressions is produced during or following thepre-drying or during or following the curing of the active material.This has the advantage of the active material already being somewhatharder and more brittle, and thus allowing the desired cracked structureto be produced more easily and faster. Curing as relates to themanufacturing of rechargeable batteries refers to the final hardening ofthe active material as is then found on the finished electrode plate.

According to one advantageous further development of the invention, themechanical impacting is effected with rounded profile contours and/orsharp-edged profiles. Particularly when the above-cited press is used,the surface of same can have sharp-edged profiles. Using rounded profilecontours has the advantage of producing the pattern of slot-shapeddepressions in a relatively gentle manner and being better able toprevent unwanted damaging of the electrode plate. Wasting of activematerial from the electrode plate in response to the mechanical impactis in particular prevented, e.g. due to falling or being forced out ofindividual window-like cutouts. A wave profile in particular can be usedfor the rounded profile contour, e.g. in the form of staggered rollerbelts, individual cylindrical rollers or spheres or semi-spheres.

With respect to sharp-edged profiles, these can be e.g. blade orneedle-shaped, for example in the form of a piercing unit or a networkof blades.

In accordance with one advantageous further development of theinvention, the impacting tool for mechanically impacting the lead gridprovided with the active material thus comprises rollers, cylindersand/or spheres and/or semi-spheres, or an upper and lower press betweenwhich the lead grid provided with the active material is pressed.

According to one advantageous further development of the invention, thelead grid provided with the active material is moved in a continuousmotion relative to an impacting tool during the mechanical impacting.The impacting tool thereby performs the mechanical impacting of the leadgrid provided with the active material. The lead grid can thus becontinuously pulled or pushed through, e.g. by an impacting toolconfigured in the form of staggered roller belts. Said movement can alsobe discontinuous such that the lead grid provided with the activematerial is stationary during the mechanical impact and moved relativeto the impacting tool prior to and subsequent the mechanical impact.This is particularly advantageous when the above-cited press is used tointroduce the pattern of slot-shaped depressions. In this case, the leadgrid to be processed can be automatically driven into a machiningstation in which the presses are arranged, the presses then operated,and thereafter, after the presses retreat again, the lead grid providedwith the pattern of slot-shaped depressions removed from the machiningstation.

According to one advantageous further development of the invention, thedepressions are produced in the electrode plate's horizontal directionof extension and/or vertical direction of extension, in each caserelative to the electrode plate's mounting orientation in a rechargeableelectrochemical battery in the battery's normal position according tospecifications. As a general rule, a horizontal alignment to the bottomof the battery is the battery's normal position according tospecifications. The depressions can also run in a combined horizontaland vertical direction of extension; i.e. diagonally at differentangles.

The pattern of slot-shaped depressions can thereby form an irregular,network-like structure or a regular structure. The individualdepressions can merge into one another, intersect or run separately fromother depressions.

The task as initially specified is further solved in accordance withclaim 9 by an installation for producing an electrode plate of arechargeable electrochemical battery, whereby the electrode platecomprises a substantially flat lead grid having a plurality of grid barsand a plurality of window-like cutouts formed between the grid bars andactive material introduced into the cutouts and/or on the grid bars ofthe lead grid, wherein the installation comprises at least one leadgrid-producing station for producing the lead grid, one pasting stationfor introducing the active material, and one depression-forming stationin which the pattern of slot-shaped depressions is produced in theactive material by mechanically impacting the lead grid provided withthe active material, wherein the depressions extend to a depth from theouter surface of the active material.

Advantageously, the lead grid-producing station and pasting stationsystem components can be further used in installations already beingused by manufacturers of such electrode plates. Only thedepression-forming station needs to be supplemented. Same comprisesinter alia an impacting tool for mechanically impacting the lead gridprovided with the active material. The impacting tool can in particularbe designed pursuant to the above-described embodiments. The citedinstallation can advantageously realize one or more of the above-citedmethods for producing an electrode plate. Accordingly, the installationcan produce an electrode plate having the advantages as specified at theoutset, particularly improved electrolyte absorbency.

According to one advantageous further development of the invention, atleast the depression-forming station has a housing to shield theelectrode plate from the surroundings at least during mechanicalimpacting. This has the advantage of shielding the surroundings from anypossible contaminants which may be discharged during production of theslot-shaped depressions such as e.g. lead dust.

According to one advantageous further development of the invention, theinstallation comprises a plate-smoothing station which is arrangeddownstream of the depression-forming station with respect to theprocessing sequence. The electrode plates being processed in theinstallation thus arrive at the plate-smoothing station after beingmachined in the depression-forming station. The electrode plates areexternally smoothed again in the plate-smoothing station prior tofurther processing. This has the advantage of the electrode plates thusagain being compatible with further manufacturing process steps andthese being able to be performed without any change to the manufacturingprocess. The pattern of the slot-shaped depressions in the activematerial is however thereby retained.

The plate-smoothing station can be arranged together with thedepression-forming station in the above-described housing.

The depression-forming station can be arranged in the installation atthe point where the electrode plates are separated for the first timeafter curing, e.g. directly before the wrapping machine in which theelectrode plates are wrapped in the separator material. The plateseparation there can for example proceed to the depression-formingstation and from there into the wrapping machine feed. Since these typesof installations already protect personnel from lead dust at this point,no additional lead dust extraction measures are required. Thedepression-forming station can be introduced into the manufacturingprocess virtually anywhere subsequent pasting; i.e. subsequent theintroducing of the active material, up until the point the plate set isinserted into the battery case. In particular, mechanical impacting toproduce the pattern of slot-shaped depressions can also not occur untilthe electrode plate is already wrapped in the separator material.

The task as initially specified is further solved in accordance withclaim 10 by an electrode plate of a rechargeable electrochemicalbattery, whereby the electrode plate comprises a substantially flat leadgrid having a plurality of grid bars and a plurality of window-likecutouts formed between the grid bars and active material introduced intothe cutouts and/or on the grid bars of the lead grid, whereby the activematerial has an artificially produced pattern of slot-shaped depressionson its surface, wherein the depressions extend to a depth from the outersurface of the active material.

The task as initially specified is further solved in accordance withclaim 11 by a rechargeable electrochemical battery having at least oneelectrode plate of the above-cited type.

The following will reference the drawings in describing the invention ingreater detail based on example embodiments.

Shown are:

FIG. 1: a semi-exploded view of a rechargeable electrochemical batteryas well as its components;

FIG. 2: a lead grid;

FIG. 3: a lead grid provided with an active material;

FIG. 4: the wrapping of a lead grid provided with an active materialwithin a separator;

FIG. 5: an installation for producing an electrode plate;

FIGS. 6-9: embodiments of an impacting tool having a rounded profile;and

FIG. 10: a stamping press.

The figures provide like elements with like reference numerals.

An example of the fundamental structure of a rechargeable battery 100according to the invention will first be described with reference toFIG. 1. The rechargeable battery 100 can in particular be implemented asa lead-acid battery having liquid electrolyte, e.g. in the form ofsulfuric acid. The rechargeable battery 100 comprises a case 110 inwhich one or more plate packs 107 are arranged. The rechargeable battery100 has a specified number of plate packs 107 corresponding to itsnumber of cells. The plate packs 107 are each arranged in individualholding chambers of case 110 separated from each other by partitionwalls. The plate packs 107 are connected together into a seriesconnection within the case 110 by internal connecting elements (notdepicted in FIG. 1). The positive plates of a plate pack on one end andthe negative plates of the other plate pack on the other end are in eachcase electrically connected to respective external terminals 108, 109provided in a cover piece 111 of the rechargeable battery case 110. Theelectrical energy of the battery 100 for electrical loads is suppliedthrough terminals 108, 109.

The plate packs 107 exhibit respectively alternating positive andnegative electrode plates. The negative electrode plates are shown asnegative plate set 115, the positive electrode plates as positive plateset 114. FIG. 1 still depicts some individual electrode plates inexemplification; i.e. negative electrode plate 105 having a negativeflat lead grid 102 and positive electrode plate 104 having a positiveflat lead grid 101. The positive electrode plate 104 and the negativeelectrode plate 105 depicted in FIG. 1 have already been provided with apasting of active material, covering the individual grid bars andcutouts. The positive and/or negative lead grid comprise(s) a pluralityof grid bars and a plurality of window-like cutouts formed between thegrid bars. The positive and/or negative lead grid 101, 102 can beproduced for example by a stamping process or by another method such ascasting and/or rolling.

The positive electrode plate 104 is additionally separated from thenegative electrode plate 105 by a separator material 106. The separatormaterial 106 can in particular be designed in the form of a wrappingwhich holds the positive electrode plate 104 and separates it fromadjacent electrode plates.

The positive electrode plates 104 comprise respective connection tabs103, by means of which the electrode plates in the positive plate set114 are connected together in a parallel connection. The negativeelectrode plates 105 comprise respective connection tabs 103, by meansof which the electrode plates in the negative plate set 115 areconnected together in a parallel connection. The connection can be madeby a connector 112 which is soldered or welded onto the connection tabs103 as is visible in FIG. 1.

The rechargeable battery 100 according to FIG. 1 can in particularcomprise one or more inventive electrode plates, e.g. in the form ofpositive electrode plates 104.

FIG. 2 shows an example of a positive lead grid 101 in plan view. It canbe seen that the lead grid 101 comprises a plurality of grid bars 121,between which are found a plurality of window-like cutouts 113. To makeit easier to handle and to provide mechanical stabilization as well asimprove its electrical properties, the outer edge of the lead grid 101can exhibit one, multiple or all of the following cited frame sections:upper frame section 120, left side frame section 119, lower framesection 117, right side frame section 118.

FIG. 3 shows the lead grid 101 from FIG. 2 after having been at leastpartly covered with active material, usually applied in paste form. Thisprocess is also known as pasting. FIG. 4 shows the lead grid 103 of FIG.3 provided with the active material being inserted into a wrapper-shapedseparator 106.

FIG. 5 depicts an installation for producing an electrode plate,particularly a positive electrode plate 104 as described above, inschematic representation. The installation comprises various stations 1,2, 3, 4, 5, 6, specifically a lead grid-producing station 1, a pastingstation 2, a separating station 3, a storage station 4, adepression-forming station 5 and a smoothing station 6. The individualstations 1, 2, 3, 4, 5, 6 are, as FIG. 5 shows, successively arrangedsuch that the raw material 14 fed into lead grid-producing station 1will be processed step by step into the resulting electrode plate.

The lead grid-producing station 1 processes the pig lead supplied to itinto a double-strand grid strip 10. This can be realized in leadgrid-producing station 1 by means of a casting process, a rollingprocess and/or a stamping process. The double-strand grid strip 10 hasan upper and a lower strand of lead grid 101 which are still contiguous.The upper and lower strand are additionally connected together by theconnection tabs 103 of the lead grid 101. The double-strand grid strip10 is still to be separated into the individual lead grids 101 later on.

First, however, the active material can be introduced in pasting station2, producing the double-stranded pasted grid strip 11 as depicted inFIG. 5.

According to FIG. 5, the separating station 3 follows the pastingstation 2. However, this is just one possible embodiment of the depictedinstallation. The separating station can for example also bealternatively arranged after smoothing station 6. For now, however, theembodiment as depicted in FIG. 5 is assumed. Individual lead grids 104provided with active material are separated from the double-strandpasted grid strip in separating station 3, and are also identified inFIG. 5 by reference numeral 12.

The electrode plate 12, or respectively its active material inparticular, can be pre-dried, as well as cured as applicable, beforesaid electrode plate 12 is fed to depression-forming station 5. To thisend, the electrode plate 12 can be stored temporarily, e.g. in storagestation 4. Alternatively, further processing in depression-formingstation 5 can also follow immediately.

The slot-shaped depressions are produced in the active material indepression-forming station 5 by the electrode plate 12 being subjectedto mechanical impact. The electrode plate 12 is then subsequentlymachined in the smoothing station 6 so as to again effect an externalsmoothing of the active material, e.g. by passing the electrode plate 12through a pair of rollers. Ultimately exiting the smoothing station 6 isan electrode plate 13 having the pattern 15 of slot-shaped depressionsas seen in FIG. 5.

The electrode plate can alternatively be wrapped in the separator 106either before or after the processing occurring in depression-formingstation 5. To this end, the installation additionally comprises anappropriately situated wrapping station (not shown in FIG. 5), e.g. inthe form of the above-cited wrapping machine.

If the separating station 3 is not arranged until after the smoothingstation 6, the grid strip 11 is guided past the impacting tool of thedepression-forming station 5, for example in a continuous motion. Theimpacting tool can then be designed as will be clarified below withreference to FIGS. 6 to 9.

The depression-forming station 5 can be enclosed in a housing 7 in orderto trap emissions, e.g. lead dust, from the surroundings. The smoothingstation 6 can also be arranged inside the housing 7.

FIGS. 6 to 9 show embodiments of the impacting tool ofdepression-forming station 5 with which the lead grid provided with theactive material is mechanically impacted in order to produce the patternof slot-shaped depressions in the active material. FIG. 6 shows anembodiment of the impacting tool 8 in a side view. The impacting tool 8comprises an upper set 84 of rollers 80 as well as a lower set 85 ofrollers 80. The rollers 80 of the upper and lower set 84, 85 arearranged close together vertically or even overlap. The rollers 80 of arespective set 84, 85 have a greater distance from one anotherhorizontally than they do vertically. The upper set 84 of rollers 80 isdisposed opposite from the lower set 85 of rollers 80 at an offset. Agrid strip 11, likewise depicted in side view in FIG. 6, led through therollers 80 will thereby be curved into the wave-shaped form seen in FIG.6. The rollers which are present after the grid strip 11 exits out ofthe impacting tool 8 can smooth the wave form out again into asubstantially flat grid strip from which flat electrode plates can beproduced. The impacting tool according to FIG. 6 is particularly wellsuited to a continuous feed of the lead grid or grid strip 11respectively.

FIGS. 7 to 9 depict embodiments of sections of the impacting tool 8 asviewed from above; i.e. onto the upper set 84 of rollers. According toFIG. 7, each roller 80 has a cylindrical impacting body 82 mounted on arotational axis 81. In one embodiment according to FIG. 8, the rollers80 have spherical impacting bodies 83 arranged on a rotatable spindle81. Instead of having a spherical form, the impacting bodies 83 can alsohave a different form such as an elliptical or angular form.

According to FIG. 9, a plurality of the spherical impacting bodiesdepicted in FIG. 8 are arranged adjacently, whereby the individualadjacent rows of the spherical impacting bodies are disposed at anoffset from one another. FIG. 9 for example shows the upper section 84of the impacting tool of FIG. 6. The lower section 85 can be ofcomparable design.

FIG. 10 shows one embodiment of an impacting tool as a stamping press 9.This embodiment is particularly suited to discontinuous electrode plate12 movement, e.g. for already separated electrode plates 12. Theelectrode plate 12 to be processed is fed in as per arrow 92 anddeposited on a lower die 90 of the stamping press 9. Although the lowerdie 90 can be stationary, as shown in FIG. 10, it can also be configuredas a movable lower die. An upper press 91 is moved downward onto theelectrode plate 12 as per the depicted arrow. The electrode plate 12 isthen pressed between the upper press 91 and the lower die 90. Thesurface area provided on the upper press 91 and the lower die 90 forpressing the electrode plate thereby exhibits a structure which resultsin the pattern of slot-shaped depressions being produced in the activematerial of the electrode plate 12. The upper press 91 thereafter raisesagain and the electrode plate 12 is advanced in the direction of arrow93.

The invention claimed is:
 1. A method for producing an electrode plateof a rechargeable electrochemical battery having the following stepsperformed in the following order: a) producing a substantially flat leadgrid having a plurality of grid bars and a plurality of window-likecutouts formed between the plurality of grid bars, wherein the pluralityof grid bars and the plurality of window-like cutouts form a pattern; b)introducing an active material into the plurality of window-like cutoutsand/or onto the plurality of grid bars of the lead grid to form anexternal surface of the electrode plate; and c) creating slot-shapeddepressions in the active material by mechanically impacting the leadgrid provided with the active material using a mechanical impactor,wherein mechanically impacting the lead grid provided with the activematerial using the mechanical impactor comprises forming contact betweenthe lead grid provided with the active material and the mechanicalimpactor, wherein the slot-shaped depressions extend to a depth from theexternal surface of the electrode plate in a vertical direction towardthe plurality of grid bars, wherein the slot-shaped depressions are anirregular, network-like structure on the external surface, wherein theirregular, network-like structure on a portion of the external surfaceis different from an impacting surface of the mechanical impactor havingcontacted the portion of the external surface, and wherein theslot-shaped depressions are configured to overlap with a grid bar of theplurality of grid bars with respect to the vertical direction.
 2. Themethod according to claim 1, wherein the slot-shaped depressions arerealized only by mechanically impacting the active material.
 3. Themethod according to claim 1, wherein mechanically impacting the leadgrid occurs during or following pre-drying or during or following curingof the active material.
 4. The method according to claim 1, wherein theimpacting surface of the mechanical impactor comprises sharp-edgedprofiles.
 5. The method according to claim 1, wherein the lead gridprovided with the active material is moved in a continuous motionrelative to the mechanical impactor while the lead grid is mechanicallyimpacted and/or the mechanical impactor is moved in discontinuous motionsuch that the lead grid provided with the active material is stationarywhile the lead grid is mechanically impacted and moved relative to themechanical impactor prior to and subsequent to mechanically impactingthe lead grid.
 6. The method according to claim 1, wherein theslot-shaped depressions are produced in a horizontal direction ofextension relative to the mounting orientation of the electrode plate ina rechargeable electrochemical battery in a horizontal alignment to abottom of the battery.
 7. The method according to claim 1, wherein themechanical impactor for mechanically impacting the lead grid providedwith the active material comprises rollers, cylinders, and/or spheres.8. The method according to claim 1, wherein the impacting surface of themechanical impactor comprises a rounded profile.
 9. The method accordingto claim 1, wherein the impacting surface of the mechanical impactor issmooth.
 10. The method according to claim 1, wherein the slot-shapeddepressions are created directly as a result of mechanically impactingthe lead grid provided with the active material.
 11. The methodaccording to claim 1, wherein the mechanical impactor for mechanicallyimpacting the lead grid provided with the active material comprises anupper press and a lower press, and wherein the lead grid provided withthe active material is pressed between the upper press and the lowerpress to create the slot-shaped depressions.
 12. The method according toclaim 1, comprising smoothing the lead grid provided with the activematerial and having the slot-shaped depressions after creating theslot-shaped depressions.